http://www.pinknews.co.uk/2014/07/11/world-health-organization-hiv-prevention-urgently-needed-for-msm-and-transgender-people/
I'm curious why the numbers are so much higher among gay/bi men and trans women. Are we really having that much more sex? Are we having more unprotected sex? I'm sure this is probably a dumb question, coming from someone who has only ever had sex with one person, and never plans on having sex again. And if I do, it would only be with women.
The history of this is really complex and would take a really long time to write out; however, the pre-HIV/AIDS era has a lot to do with the current epidemic.
I'm gonna try to keep this kosher.
Essentially, for gay/bi men and preop transwomen, if you want to achieve penetration, you have to use the anal passage. The rectal walls are much more likely to tear, exposing participants to the virus both ways, assuming its presence. A condom goes a long way in stopping this flow of the virus, but even they have their limits. It's just a risk you take.